Washington -LRB- CNN -RRB- -- Senior Navy enlistees seeking credentials to train others on using nuclear reactors that power carriers and subs are under investigation for cheating on an exam that may have involved classified information , top military officials said Tuesday .

The troubling disclosure comes just weeks after the Air Force alleged widespread cheating on a proficiency test by officers with oversight responsibilities for nuclear missiles . Both involved written exams .

`` To say that I 'm disappointed would be an understatement , '' Adm. Jonathan Greenert , the chief of naval operations , said at a news conference .

Staff at the Naval Nuclear Propulsion Program in Charleston , South Carolina , allegedly shared information about the test on reactor operations among themselves , officials said of their findings so far .

There is no indication students were involved .

The allegations came to light after a sailor in the unit came forward to share his concerns about potential dishonesty on exams .

Navy responds to allegations

About 30 naval engineering watch supervisors have been decertified , meaning they can not carry out certain duties , according to a Navy official .

Those cited had previously been certified on nuclear systems , gone to sea , returned to shore duty and had to be certified as instructors to stand watch at training reactors .

Navy officials said staff must qualify to operate and instruct students on a training reactor .

The last incident of this kind occurred in 2010 aboard a sub , Navy officials said .

Adm. John Richardson , director of the propulsion program , said the investigation is ongoing but did not disclose what information may have been exchanged .

`` But it 's fair to say that these exams and the operation of the plants do involve classified information and that will be an active part of the investigation to fully understand that , '' he said .

Navy officials stressed that the nuclear propulsion systems are not related to nuclear weapons .

The Air Force scandal has swept up 92 officers at Malmstrom Air Force Base . That case involves a proficiency test .

Some of those involved are accused of cheating on the test via text messaging last summer while others are accused of not speaking up about it .

Air Force Secretary Deborah Lee James described hearing about a culture for perfection within that unit that created a climate of undue stress and fear .

But Richardson saw no parallels with the Air Force on that issue .

Air Force cheating scandal

`` With respect to the morale and the necessity to pass these exams in order to advance , that 's not really a dimension of our program , '' he said .

CNN 's Barbara Starr contributed to this report .

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Navy cheating follows scandal at Air Force nuclear base over proficiency exam

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The Navy case involves enlistees testing to use nuclear reactors that power ships and subs

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About 30 people have lost their authority to perform certain duties